Structure of VCSEL and method for manufacturing the same

ABSTRACT

A vertical-cavity surface-emitting Laser (VCSEL) has a three-trench structure. By forming a first trench within a mesa around the periphery of an output window of the VCSEL, the overall capacitance is decreased and the time used in the oxidation process for an oxidation layer is shortened. By forming a second trench and a third trench on the periphery of the mesa in a step-like concave manner, the mesa becomes a step-like structure having double mesa-layers. Such that, a larger heat-radiating area can be obtained for decreasing thermal effects, while the metal-gap defects of the metal layer can also be avoided. The implant layer is formed around the periphery of the output window for controlling the optical mode and confining the current path. In addition, an output layer is formed on the output window for controlling the output light.

This application claims the benefit of Taiwan Patent Application SerialNo. 106104272, filed on Feb. 9, 2017, the subject matter of which isincorporated herein by reference.

BACKGROUND OF INVENTION 1. Field of the Invention

The invention relates to a structure of VCSEL and a method formanufacturing the same, and more particularly to the VCSEL structure andthe method for manufacturing the VCSEL structure that introduce athree-trench structure to reduce overall capacitance and shorten timefor oxidation process.

2. Description of the Prior Art

The VCSEL (Vertical Cavity Surface Emitting Laser) is one of emittinglaser diodes. Since the VCSEL needs smaller power and is less expensive,the features of higher speeds and lower cost have made the VCSEL popularin local networking. Light-emitting and light-detecting materials forproducing the VCSEL include mainly GaAs and InP. Generally, themetal-organic chemical vapor deposition (MOCVD) is adopted to producethe epitaxial wafer for the VCSELs. In comparison with a typicaledge-emitting laser, the resonant chamber and mirrors for reciprocallyexciting photos in the resonant chamber of the VCSEL are not the crystallattice boundaries naturally formed during the manufacturing process,but already formed during the growth of the epitaxy of the epitaxialwafer for the VCSELs.

Generally, a typical VCSEL structure largely includes a light-emittingactive layer, a resonant chamber and two distributed Bragg reflectors(DBR) with high reflectivity. When photos are generated in thelight-emitting active layer, they would oscillate reciprocally insidethe resonant chamber. As soon as any photo reaches the populationinversion, a corresponding laser light would be formed on a surface ofthe VCSEL. Since the VCSEL adopts a surface-emitting laser, the inducedlaser light would be shaped into a cone, which is easier to couple withan optical fiber, without additional optical lens. For basicstructuring, manufacturing and operating of the conventional VCSELstructure, please refer to U.S. Pat. No. 4,949,350 and U.S. Pat. No.5,468,656.

This invention is provided to improve the aforesaid conventional VCSELstructure. By introducing a specific three-trench structure, the overallcapacitance and to shorten the time for oxidation process can bereduced. Also, an ion-implanted layer at a periphery of an output windowis used to control the optical modes and to confine the current path.Further, the output window is formed on a power output layer to controlthe output light. In addition, a step-like structure having doublemesa-layers is furnished to conduct the heat and thereby to reducethermal effects.

SUMMARY OF THE INVENTION

Accordingly, it is the primary object of the present invention toprovide a structure of VCSEL and a method for manufacturing the same,that can utilize a specific three-trench structure for reducing theoverall capacitance and shortening the time for oxidation process, andfurther form a step-like structure having double mesa-layers to reducethe thermal effects.

It is another object of the present invention to provide a structure ofVCSEL and a method for manufacturing the same, that can use anion-implanted layer at a periphery of an output window to control theoptical mode and to confine the current path. In addition, a poweroutput layer is formed on the output window for controlling the outputlight, in which the power output layer is made of a dielectric materialwith a reflective index ranging 1.5˜2.0; for example, SiO₂, SiN or amixture of the aforesaid two.

In the present invention, the VCSEL structure includes a substrate, afirst mirror layer on the substrate, an active region on the firstmirror layer, a second mirror layer on active region, an oxide layer inthe second mirror layer, a mesa, a first isolation trench, a secondisolation trench, a third isolation trench, a dielectric material, afirst contact layer, and a second contact layer.

The mesa on the substrate is structured by at least a portion of thefirst mirror layer, the active region, the second mirror layer and theoxide layer. The output window is included in a central area of a topsurface of the mesa. The first isolation trench in the mesa circles atleast a portion of a periphery of the output window, and penetratesdownward through the second mirror layer, the oxide layer and the activeregion from the top surface of the mesa. The second isolation trenchcircles at least another portion of the periphery of the mesa, is spacedfrom the first isolation trench by a gap, penetrates downward at leastthrough the second mirror layer and the oxide layer, and has a bottomportion thereof located either in the active region or at the firstmirror layer. The third isolation trench circles at least a furtherportion of the periphery of the mesa, is concave from the bottom portionof the second isolation trench, penetrates downward at least through thefirst mirror layer, and has a bottom portion thereof to be located atthe substrate. The dielectric material at least fills the firstisolation trench, the first contact layer is located on the top surfaceof the mesa by contacting the second mirror layer. The second contactlayer is at least located on the bottom portion of the third isolationtrench by contacting at least the substrate.

In one embodiment of the present invention, the VCSEL structure furtherincludes an isolating layer covering at least a portion of an outersurface of the mesa, and at least a portion of the first contact layerand the second contact layer are exposed out of the isolating layer; thefirst mirror layer is an n-type distributed Bragg reflector (DBR) layer,while the second mirror layer is a p-type DBR layer; materials of thefirst mirror layer and the second mirror layer include AlGaAs withvarious Al mole percentages, wherein the oxide layer of the secondmirror layer contains Al with a relative high mole percentage; the oxidelayer at least extends horizontally from an inner rim of the firstisolation trench toward a center of the mesa; the dielectric material isa polymer material with low dielectric properties; and, the firstcontact layer and the second contact layer are both metal layers.

In one embodiment of the present invention, the VCSEL structure furtherincludes an ion-implanted region located in the second mirror layer bybeing close in height to or overlapping the oxide layer. Theion-implanted region inside the mesa is located between the outputwindow and the first isolation trench by circling at least a portion ofa periphery of the output window. Also, the first contact layer contactsan upper surface of the second mirror layer.

In one embodiment of the present invention, the VCSEL structure furtherincludes a power output layer located on the output window on the topsurface of the mesa.

In one embodiment of the present invention, the second contact layer isextended upward to an upper surface of the second mirror layer alongrespective oblique surfaces of the third isolation trench and the secondisolation trench from the bottom portion of the third isolation trench,such that a top surface of the second contact layer is largely flushwith the first contact layer, and a plane is formed at the bottomportion of the second isolation trench so as to have the second contactlayer to be in a horizon-extending state at the bottom portion of thesecond isolation trench.

In another aspect of the present invention, the method for manufacturinga VCSEL structure, includes the steps of:

performing a semiconductor process on a laser-chip base material so asto have the laser-chip base material to include, in an upward order, asubstrate, a first mirror layer on the substrate, an active region onthe first mirror layer, and a second mirror layer on the active region;

performing a first mask manufacturing process through a first mask toform a first mask layer with a first predetermined pattern on and anupper surface of the second mirror layer, wherein the firstpredetermined pattern is respective to a pattern of the first mask;

performing an ion-implanting process to form an ion-implanted region inan area of the second mirror layer uncovered by the first photoresistlayer, wherein a bottom portion of the ion-implanted region is spacedfrom the active region by a predetermined height;

with the first mask layer unremoved, performing a second maskmanufacturing process through a second mask to form a second mask layerwith a second predetermined pattern on the upper surface of the secondmirror layer and the first mask layer, wherein the second predeterminedpattern is respective to a pattern of the second mask;

performing a first etching process to form a first isolation trench byetching an area of the second mirror layer, the active region and thefirst mirror layer covered by the second mask layer, wherein the firstisolation trench penetrates downward through the second mirror layer andthe active region from the upper surface of the second mirror layer soas to have a bottom portion of the first isolation trench located at thefirst mirror layer;

performing an oxidating process through the first isolation trench toform an oxide layer extending horizontally in the second mirror layer,wherein the oxide layer is close in height to or overlapping the bottomportion of the ion-implanted region;

performing a second etching process to form a second isolation trench onthe second mirror layer, wherein the second isolation trench penetratesdownward at least through the second mirror layer and the oxide layerfrom the upper surface of the second mirror layer so as to locate abottom portion of the second isolation trench in the active region or atthe first mirror layer; and, performing a metal coating process to forma contact pad in a predetermined area on the upper surface of the secondmirror layer;

performing a third etching process to form a concave third isolationtrench at the bottom portion of the second isolation trench, wherein thethird isolation trench penetrates downward at least through the firstmirror layer so as to locate a bottom portion of the third isolationtrench at the substrate; and

filling a dielectric material into the first isolation trench, andforming an isolating layer, a first contact layer and a second contactlayer respectively in specific areas on the laser-chip base material;

wherein a mesa is defined on the laser-chip base material by the secondisolation trench and the third isolation trench, each of the secondisolation trench and the third isolation trench circles at least acorresponding portion of a periphery of the mesa, the mesa on thesubstrate consists of at least a portion of the first mirror layer, theactive region, the second mirror layer and the oxide layer, an outputwindow is formed in a central area on a top surface of the mesa, thefirst isolation trench located in the mesa circles at least a portion ofa periphery of the output window and is spaced from the second isolationtrench by a gap, and the first isolation trench penetrates downward atleast through the second mirror layer, the oxide layer and the activeregion from the top surface of the mesa;

wherein the first contact layer located on the top surface of the mesacontacts the second mirror layer, the second contact layer at leastlocated at the bottom portion of the third isolation trench at leastcontacts the substrate, the second contact layer is extended upward tothe upper surface of the second mirror layer along respective obliquesurfaces of the third isolation trench and the second isolation trenchfrom the bottom portion of the third isolation trench such that a topsurface of the second contact layer is largely flush with the firstcontact layer, and a portion of the first contact layer and the secondcontact layer is at least exposed out of the isolating layer.

All these objects are achieved by the structure of VCSEL and the methodfor manufacturing the same described below.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will now be specified with reference to itspreferred embodiment illustrated in the drawings, in which:

FIG. 1 is a schematic cross-sectional view of a preferred embodiment ofthe VCSEL structure in accordance with the present invention;

FIG. 2A is a schematic view of a first stage of a preferred method formanufacturing the VCSEL structure in accordance with the presentinvention;

FIG. 2B is a schematic view of an embodiment of the pattern for thefirst mask in accordance with the present invention;

FIG. 3A is a schematic view of a second stage of the preferred methodfor manufacturing the VCSEL structure in accordance with the presentinvention;

FIG. 3B is a schematic view of an embodiment of the pattern for thesecond mask in accordance with the present invention;

FIG. 4 is a schematic view of a third stage of the preferred method formanufacturing the VCSEL structure in accordance with the presentinvention;

FIG. 5 is a schematic view of a fourth stage of the preferred method formanufacturing the VCSEL structure in accordance with the presentinvention;

FIG. 6 is a schematic view of a fifth stage of the preferred method formanufacturing the VCSEL structure in accordance with the presentinvention; and

FIG. 7 is a schematic view of a six stage of the preferred method formanufacturing the VCSEL structure in accordance with the presentinvention.

DESCRIPTION OF THE PREFERRED EMBODIMENT

The invention disclosed herein is directed to a structure of VCSEL and amethod for manufacturing the same. In the following description,numerous details are set forth in order to provide a thoroughunderstanding of the present invention. It will be appreciated by oneskilled in the art that variations of these specific details arepossible while still achieving the results of the present invention. Inother instance, well-known components are not described in detail inorder not to unnecessarily obscure the present invention.

The structure of VCSEL and the method for manufacturing the same inaccordance with the present invention mainly applies a specificthree-trench structure to reduce the overall capacitance and to shortenthe time for oxidation process, such that a step-like structure havingdouble mesa-layers can be formed to reduce the thermal effects Inaddition, an ion-implanted layer at a periphery of an output window isused to control the optical modes and to confine the current path, andalso the output window is formed on a power output layer to control theoutput light.

Referring now to FIG. 1, a schematic cross-sectional view of a preferredembodiment of the VCSEL stricture in accordance with the presentinvention is shown.

In this embodiment, the VCSEL structure is constructed on a laser-chipbase material mainly made of a GaAs or InP material. The base materialincludes, in an upward order, a substrate 10, a first mirror layer 21located on the substrate 10, an active region 22 located on the firstmirror layer 21, and a second mirror layer 23 located on the activeregion 22. Within the second mirror layer 23, an oxide layer 231 islocated. In this embodiment, the first mirror layer 21 is an n-typedistributed Bragg reflector (DBR) layer, or called as a lower mirror. Onthe other hand, the second mirror layer 23 is a p-type DBR layer, orcalled as an upper mirror layer. Both the first mirror layer 21 and thesecond mirror layer 23 contain multi-layer structures made of AlGaAswith various Al mole percentages. In particular, the oxide layer 231 ofthe second mirror layer 23 contains Al with a relative high molepercentage. Thereupon, while in the oxidation process, the oxide layer231 can form an insulation Al₂O₃ layer.

In the VCSEL structure of the present invention, the base materialfurther includes a mesa 30, a first isolation trench 31, a secondisolation trench 32, a third isolation trench 33, a dielectric material26, a first contact layer 270, a second contact layer 271˜273, anion-implanted region 24, an isolating layer 25 and a power output layer274.

The mesa 30 located on the substrate 10 is made up of at least a portionof the first mirror layer 21, the active region 22, the second mirrorlayer 23 and the oxide layer 231. An output window 300 is formed at acentral area of a top surface of the mesa 30. In this embodiment, theoxide layer 231 is high enough to be close to a bottom portion of theion-implanted region 24, and even part thereof is overlapping a bottomportion of the ion-implanted region 24.

The first isolation trench 31 is located in the mesa 30, and circles atleast a portion of the periphery of the output window 300. The firstisolation trench 31 extends downward from the top surface of the mesa30, and penetrates at least the second mirror layer 23, the oxide layer231 and the active region 22, such that the bottom portion of the firstisolation trench 31 can reach the first mirror layer 21.

The second isolation trench 32 circles at least a portion of theperiphery of the upper part of the mesa 30, and is spaced from the firstisolation trench 31 by a gap. The second isolation trench 32 extendsdownward to penetrate at least the second mirror layer 23 and the oxidelayer 231, such that a bottom portion 321 of the second isolation trench32 can be located at one of the active region 22 and the first mirrorlayer 21. The oxide layer 231 extends horizontally from an inner rim ofthe first isolation trench 31 toward the center of the mesa 30.

The third isolation trench 33 circles at least a portion of theperiphery of the lower part of the mesa 30, and is concave down from thebottom portion 321 of the second isolation trench 32. Also, the thirdisolation trench 33 penetrates downward at least the first mirror layer21 (or penetrates the active region 22 and the first mirror layer 21),such that a bottom portion 331 of the third isolation trench 33 can belocated at the upper surface of the substrate 10.

In this embodiment, the dielectric material 26, preferable a polymermaterial with low dielectric properties, is to fill at least the firstisolation trench 31 so as to reduce the overall capacitance of the VCSELstructure. In this embodiment, the dielectric material 26 is a polymer,for example a polymide, with a reflective index of 1.5˜1.6. In thispresent invention, the resort of digging out the first isolation trench31 and then filling with a polymer (dielectric material 26) can reducesubstantially the area of the semiconductor material that is featured ina high dielectric index, and thereby the corresponding capacitance canbe reduced. The first contact layer 270 and the second contact layer271˜273 is part of the metal layer 27. The first contact layer 270 islocated on the top surface of the mesa 30, and contacts an upper surface240 of the second mirror layer 23. The second contact layer 271, 272,273 is at least located at the bottom portion 331 of the third isolationtrench 33, and at least contacts the substrate 10. In this embodiment,the second contact layer 271, 272, 273 is extended upward to the uppersurface 240 of the second mirror layer 23 along respective obliquesurfaces of the third isolation trench 33 and the second isolationtrench 32 from the bottom portion 331 of the third isolation trench 33,such that a top surface 2710 of the second contact layer 271, 272, 273can be largely flush with the top surface of the first contact layer270. Hence, in the present invention, the first contact layer 270 andthe second contact layer 271, 272, 273 are both located one the samesurface of the substrate 10, and also reach substantially the sameheight, from which the following wire bonding could be much easier. Inaddition, a plane is formed at the bottom portion 321 of the secondisolation trench 32, and thus the second contact layer 271, 272, 273 canbe in a horizon-extending state at the bottom portion 321 of the secondisolation trench 32. Thereupon, a step-like structure having doublemesa-layers an thus be formed to provide a broader lower mesa forenlarging the heat-radiating area and thereby for better reducing thethermal effects. Also, the two-stage concave second and third isolationtrenches 32, 33 contribute to reduce the slopes of the correspondingoblique surfaces, and further the bottom portion 321 of the secondisolation trench 32 is formed as a plane, such that, while the secondcontact layer 271, 272, 273 is under plating, sputtering or evaporatingfor forming the metal layer, possible metal-gap defects can beeffectively prevented.

The ion-implanted region 24 in the second mirror layer 23 is locatedabove the active layer 22. In this embodiment, part of the bottomportion of the ion-implanted region 24 is overlapped with the oxidelayer 231. By varying corresponding aperture size of the oxide layer 231and the ion-implanted region 24, the optical mode can thus becontrolled. In the present invention, the ion implantation isgain-guided, but the oxidation is index-guided. The control of theoptical mode can be achieved by the hybrid application of the ionimplantation process and the oxidation process. Further, theion-implanted region 24 in the mesa 30 is located between the outputwindow 300 and the first isolation trench 31 by circling at least aportion of the periphery of the output window 300. Also, the firstcontact layer 270 contacts an upper surface of the ion-implanted region24. In the present invention, additional ion-implanted layer 24 locatedat the periphery of the output window 300 can be used to control theoptical mode and to confine the current path. In this embodiment, theion-implanting process can implant protons or oxygen ion at a depth of2˜4 um.

The isolating layer 25 is to cover at least a portion of an outersurface of the mesa 30, and at least a portion of the first contactlayer 270 and the second contact layer 271, 272, 273 are exposed out ofthe isolating layer 25. The power output layer 274, located on theoutput window 300 of the top surface of the mesa 30, is to control theoutput light, according to the refractive index, thickness and opticalwavelength of the power output layer 274. In the present invention, thematerial for the power output layer 274 can be Si₃N₄, SiO₂, Si₃O₄, SiN,SiNO or the like. In particular, in this embodiment, the power outputlayer 274 can be made of a dielectric material; for example, SiO₂, SiNor a mixture of the aforesaid two with a reflective index of 1.5˜2.0.

Referring now to FIG. 2A to FIG. 7, different stages in order of apreferred embodiment of the method for manufacturing VCSEL structure areschematically shown.

As shown in FIG. 2A, a schematic view of a first stage of the preferredmethod for manufacturing the VCSEL structure in accordance with thepresent invention is schematically illustrated. In the method formanufacturing VCSEL structure of the present invention, a laser-chipbase material is consisted of, in an upward order, a substrate 10, afirst mirror layer 21 located on the substrate 10, an active region 22located on the first mirror layer 21, and a second mirror layer 23located on the active region 22. Then, a first mask manufacturingprocess is performed on a first mask so as to form a first mask layerhaving a first predetermined pattern on an upper surface 240 of thesecond mirror layer 23, in which the first predetermined pattern isrespective to the pattern 51 of the first mask. As shown in FIG. 2B, aschematic view of an embodiment of the pattern 51 for the first mask inaccordance with the present invention is illustrated. The pattern 51 ofthe first mask includes a central circle area 510 and a ring area 511circling the periphery of the central circle area 510, in which a radiusof the central circle area 510 is r1, an inner radius of the ring area511 is r2, an an outer radius of the ring area 511 is r3. The centralcircle area 510 of the first mask pattern 51 is defined at the area onthe upper surface 240 of the second mirror layer 23 respective to theoutput window 300 where is covered by the mask 5100, and the ring area511 of the first mask pattern 51 is defined at the area on the uppersurface 240 of the second mirror layer 23 where is covered by the mask5110 but not implanted by ions. The first mask layer includes the masks5100, 5110. Then, as shown in FIG. 2A, an ion-implanting process isperformed on the area of the second mirror layer 23 uncovered by thefirst mask layer (mask 5100, 5110) so as to undergo ion-implantationprocess for forming an ion-implanted region 24, where a bottom portionof the ion-implanted region 24 is spaced from the active region 22 by apredetermined height. In this embodiment, a bottom portion of theeffective ion-implanted area is partly overlapped with the oxide layer.By providing the additional ion-implanted layer 24 at the periphery ofthe output window 300 according to the present invention, the opticalmode can be controlled and the current path can be confined.

As shown in FIG. 3A, a schematic view of a second stage of the preferredmethod for manufacturing the VCSEL structure in accordance with thepresent invention is schematically illustrated. Under the circumstancesthat the first mask layers 5100, 5110 are yet to be removed, a secondmask is applied to perform a second mask manufacturing process. A secondmask layer having a second predetermined pattern is formed on the uppersurface 240 of the second mirror layer 23 and the first mask layers5100, 5110, in which the second predetermined pattern is locatedrespective to the pattern 52 of the second mask. As shown in FIG. 3B, aschematic view of an embodiment of the pattern 52 for the second mask inaccordance with the present invention is illustrated. The pattern 52 ofthe second mask includes a central circle area 520 and a periphery area521 circling the central circle area, in which a radius of the centralcircle area 520 is R1, and an inner radius of the periphery area 521 isR2. The central circle area 520 and the periphery area 521 of the secondmask pattern 52 are defined respective to the area on the upper surface240 of the second mirror layer 23 that is covered by the masks 5200,5210. The area uncovered by the masks 5200, 5210 is then etched togenerate the first isolation trench 31. In this embodiment, the secondmask layer includes the masks 5200, 5210.

In this embodiment, the radius R1 of the central circle area 520 of thesecond mask pattern 52 is ranged between the inner radius r2 of the ringarea 51 of the first mask pattern 51 and the radius r3 of the periphery(i.e., r2<R1<r3). Also, the inner radius R2 of the the periphery area521 of the second mask pattern 52 is larger than the radius r3 of theperiphery of the ring area 511 of the first mask pattern 51 (i.e.,r3<R2). Hence, while in performing the first and the second maskprocesses, self-alignment can be achieved so as to increase alignmentprecision of the aperture of the oxide layer 231 and the ion-implantedregion 24 in the following manufacturing processes.

Then, as shown in FIG. 4, a schematic view of a third stage of thepreferred method for manufacturing the VCSEL structure in accordancewith the present invention is schematically illustrated. A first etchingprocess is performed at the second mirror layer 23 to etch the uncoveredareas by the second mask layers 5200, 5210 at the active region 22 andthe first mirror layer 21, such that a first isolation trench 31, isformed. As shown, the first isolation trench 31 penetrates downward fromthe upper surface 240 of the second mirror layer 23, passes through thesecond mirror layer 23 and the active region 22, and finally reaches thefirst mirror layer 21 by a bottom portion of the first isolation trench31.

Then, as shown in FIG. 5, a schematic view of a fourth stage of thepreferred method for manufacturing the VCSEL structure in accordancewith the present invention is schematically illustrated. An oxidationprocess is performed to form an oxide layer 231 extending horizontallyin the second mirror layer 23 and passing through the first isolationtrench 31, and the oxide layer 231 is close to, preferably overlappingpartly, the ion-implanted region 24. Also, the oxide layer 231 islocated in the active region 22. In comparison with the prior art that asecond isolation trench 32 is needed for performing the oxidationprocess of the oxide layer 231 due to the absence of the first isolationtrench 31, the oxidation process of the oxide layer 231 in this presentinvention is carried out through the first isolation trench 31, which iscomparatively close in distance to the output window 300. Thus, thenecessary distance for oxidation is much shorter, and time for theoxidation process is significantly reduced. Further, possible streetconcentration problem upon the oxide layer 2 caused by long-distanceoxidation can be substantially lessened.

Then, as shown in FIG. 6, a schematic view of a fifth stage of thepreferred method for manufacturing the VCSEL structure in accordancewith the present invention is schematically illustrated. A secondetching process is performed to form a second isolation trench 32 on thesecond mirror layer 23, in which the second isolation trench 32penetrates downward from the upper surface 240 of the second mirrorlayer 23, passes at least through the second mirror layer 23 and theoxide layer 231, and finally has a bottom portion 321 of the secondisolation trench 32 to be located in the active region 22 or at thefirst mirror layer 21. In addition, a metal coating process is performedto form a contact pad in a predetermined area on the upper surface 240of the second mirror layer 23, where the contact pad would become aportion of the first contact layer 270 lately in the manufacturingprocess.

Then, as shown in FIG. 7, a schematic view of a sixth stage of thepreferred method for manufacturing the VCSEL structure in accordancewith the present invention is schematically illustrated. A third etchingprocess is performed so as to form a concave third isolation trench 33at the bottom portion 321 of the second isolation trench 32, where thethird isolation trench 33 penetrates downward at least through the firstmirror layer 21 (or through the active region 22 and the first mirrorlayer 21), and finally has a bottom portion 331 of the third isolationtrench 33 to be located at the substrate 10.

Thereafter, the first isolation trench 31 is filled with a dielectricmaterial 26 so as thereby to reduce the overall capacitance of the VCSELstructure. In addition, a power output layer 274, an isolating layer 25and a metal layer 27 (including the first contact layer 270 and thesecond contact layer 271, 272, 273) are respectively formed incorresponding relevant areas on the laser-chip base material. Thereupon,the VCSEL structure of the present invention as shown in FIG. 1 can beproduced.

In this embodiment, as shown in FIG. 1, the second isolation trench 32and the third isolation trench 33 can be used to define a mesa 30 on thelaser-chip base material, by having both the second isolation trench 32and the third isolation trench 33 to circle at least a portion of theperiphery of the mesa 300. The mesa 300, located on the substrate 10, isconsisted of at least a portion of the first mirror layer 21, the activeregion 22, the second mirror layer 23 and the oxide layer 231. In acentral area on a top surface of the mesa 300, an output window 300 islocated. The first isolation trench 31, located in the mesa 30, circlesat least a portion of the periphery of the output window 300, and isspaced from the second isolation trench 32 by a gap. The first isolationtrench 31 penetrates downward from the top surface of the mesa 30,passes at least through the second mirror layer 23, the oxide layer 231and the active region 22.

In this embodiment, the power output layer 274, located on the outputwindow 300 on the top surface of the mesa 30, is to control the outputlight. The ion-implanted region 24 is located in the second mirror layer23 at a position thereof on the oxide layer 231 with a bottom portion ofthe ion-implanted region 24 overlapping partly the oxide layer 231. Theion-implanted region 24 in the mesa 30 is located between the outputwindow 300 and the first isolation trench 31 by circling at least aportion of the periphery of the output window 300. In the presentinvention, the ion-implanted region 24 is to control the optical modeand to confine the current path.

In this embodiment, the first contact layer 270 is located on the topsurface of the mesa 30 by contacting the upper surface of the secondmirror layer 23, the second contact layer 271, 272, 273 is at leastlocated at the bottom portion 331 of the third isolation trench 33 by atleast contacting the substrate 10, and the second contact layer 271,272, 273 extends upward along respective oblique surfaces of the thirdisolation trench 33 and the second isolation trench 32 from the bottomportion 331 of the third isolation trench 33 to the upper surface of thesecond mirror layer 23, so that a top surface of the second contactlayer 271, 272, 273 can be largely flush with the first contact layer270. Thus, the first contact layer 270 and the second contact layer 271,272, 273 of the present invention are located on the same side of thesubstrate 10, and almost at the same height to convene the followingwire-bonding process. In addition, at least a portion of the firstcontact layer 270 and the second contact layer 271, 272, 273 is exposedout of the isolating layer 25. The bottom portion 321 of the secondisolation trench 32 is formed as a plane so that the second contactlayer 271, 272, 273 can be in a horizon-extending state at the bottomportion 321 of the second isolation trench 32. Thereupon, a step-likestructure having double mesa-layers can be formed so as to provide alarger lower portion to the mesa, from which the heat-radiating area canbe broader and better for reducing the thermal effects. Also, sinceoblique sidewalls of the two-step concave second and third isolationtrenches 32, 33 are less stiff and the bottom portion 321 of the secondisolation trench 32 is a plane, thus, while the second contact layer271, 272, 273 is under plating, sputtering or evaporating for formingthe metal layer, possible metal-gap defects can be effectivelyprevented.

While the present invention has been particularly shown and describedwith reference to a preferred embodiment, it will be understood by thoseskilled in the art that various changes in form and detail may bewithout departing from the spirit and scope of the present invention.

What is claimed is:
 1. A VCSEL structure, comprising: a substrate; afirst mirror layer, located on the substrate; an active region, locatedon the first mirror layer; a second mirror layer, located on activeregion; an oxide layer, located in the second mirror layer; a mesa,located on the substrate, structured by at least a portion of the firstmirror layer, the active region, the second mirror layer and the oxidelayer, an output window being included in a central area of a topsurface of the mesa; a first isolation trench, located in the mesa,circling at least a portion of a periphery of the output window,penetrating downward through the second mirror layer, the oxide layerand the active region from the top surface of the mesa; a secondisolation trench, circling at least another portion of the periphery ofthe mesa, spaced from the first isolation trench by a gap, penetratingdownward at least through the second mirror layer and the oxide layer,having a bottom portion thereof located either in the active region orat the first mirror layer; a third isolation trench, circling at least afurther portion of the periphery of the mesa, being concave from thebottom portion of the second isolation trench, penetrating downward atleast through the first mirror layer, having a bottom portion thereof tobe located at the substrate; a dielectric material, at least filling thefirst isolation trench; a first contact layer, located on the topsurface of the mesa by contacting the second mirror layer; and a secondcontact layer, at least located on the bottom portion of the thirdisolation trench by contacting at least the substrate.
 2. The VCSELstructure of claim 1, wherein: the VCSEL structure further includes anisolating layer covering at least a portion of an outer surface of themesa, and at least a portion of the first contact layer and the secondcontact layer are exposed out of the isolating layer; the first mirrorlayer is an n-type distributed Bragg reflector (DBR) layer, while thesecond mirror layer is a p-type DBR layer; materials of the first mirrorlayer and the second mirror layer include AlGaAs with various Al molepercentages, wherein the oxide layer of the second mirror layer containsAl with a relative high mole percentage; the oxide layer at leastextends horizontally from an inner rim of the first isolation trenchtoward a center of the mesa; the dielectric material is a polymermaterial with low dielectric properties; and, the first contact layerand the second contact layer are both metal layers.
 3. The VCSELstructure of claim 1, further including: an ion-implanted region,located in the second mirror layer by being close in height to oroverlapping the oxide layer, and the ion-implanted region inside themesa is located between the output window and the first isolation trenchby circling at least a portion of a periphery of the output window;wherein the first contact layer contacts an upper surface of the secondmirror layer.
 4. The VCSEL structure of claim 1, further including apower output layer located on the output window on the top surface ofthe mesa.
 5. The VCSEL structure of claim 1, wherein: the second contactlayer is extended upward to an upper surface of the second mirror layeralong respective oblique surfaces of the third isolation trench and thesecond isolation trench from the bottom portion of the third isolationtrench, such that a top surface of the second contact layer is largelyflush with the first contact layer; and, a plane is formed at the bottomportion of the second isolation trench so as to have the second contactlayer to be in a horizon-extending state at the bottom portion of thesecond isolation trench.
 6. A method for manufacturing VCSEL structures,comprising the steps of: performing a semiconductor process on alaser-chip base material so as to have the laser-chip base material toinclude, in an upward order, a substrate, a first mirror layer on thesubstrate, an active region on the first mirror layer, and a secondmirror layer on the active region; performing a first mask manufacturingprocess through a first mask to form a first mask layer with a firstpredetermined pattern on and an upper surface of the second mirrorlayer, wherein the first predetermined pattern is respective to apattern of the first mask; performing an ion-implantation process toform an ion-implanted region in an area of the second mirror layeruncovered by the first photoresist layer, wherein a bottom portion ofthe ion-implanted region is spaced from the active region by apredetermined height; with the first mask layer unremoved, performing asecond mask manufacturing process through a second mask to form a secondmask layer with a second predetermined pattern on the upper surface ofthe second mirror layer and the first mask layer, wherein the secondpredetermined pattern is respective to a pattern of the second mask;performing a first etching process to form a first isolation trench byetching an area of the second mirror layer, the active region and thefirst mirror layer covered by the second mask layer, wherein the firstisolation trench penetrates downward through the second mirror layer andthe active region from the upper surface of the second mirror layer soas to have a bottom portion of the first isolation trench located at thefirst mirror layer; performing an oxidation process through the firstisolation trench to form an oxide layer extending horizontally in thesecond mirror layer, wherein the oxide layer is close in height to oroverlapping the bottom portion of the ion-implanted region; performing asecond etching process to form a second isolation trench on the secondmirror layer, wherein the second isolation trench penetrates downward atleast through the second mirror layer and the oxide layer from the uppersurface of the second mirror layer so as to locate a bottom portion ofthe second isolation trench in the active region or at the first mirrorlayer; and, performing a metal coating process to form a contact pad ina predetermined area on the upper surface of the second mirror layer;performing a third etching process to form a concave third isolationtrench at the bottom portion of the second isolation trench, wherein thethird isolation trench penetrates downward at least through the firstmirror layer so as to locate a bottom portion of the third isolationtrench at the substrate; and filling a dielectric material into thefirst isolation trench, and forming an isolating layer, a first contactlayer and a second contact layer respectively in specific areas on thelaser-chip base material; wherein a mesa is defined on the laser-chipbase material by the second isolation trench and the third isolationtrench, each of the second isolation trench and the third isolationtrench circles at least a corresponding portion of a periphery of themesa, the mesa on the substrate consists of at least a portion of thefirst mirror layer, the active region, the second mirror layer and theoxide layer, an output window is formed in a central area on a topsurface of the mesa, the first isolation trench located in the mesacircles at least a portion of a periphery of the output window and isspaced from the second isolation trench by a gap, and the firstisolation trench penetrates downward at least through the second mirrorlayer, the oxide layer and the active region from the top surface of themesa; wherein the first contact layer located on the top surface of themesa contacts the second mirror layer, the second contact layer at leastlocated at the bottom portion of the third isolation trench at leastcontacts the substrate, the second contact layer is extended upward tothe upper surface of the second mirror layer along respective obliquesurfaces of the third isolation trench and the second isolation trenchfrom the bottom portion of the third isolation trench such that a topsurface of the second contact layer is largely flush with the firstcontact layer, and a portion of the first contact layer and the secondcontact layer is at least exposed out of the isolating layer.
 7. Themethod of claim 6, wherein: the first mirror layer is an n-typedistributed Bragg reflector (DBR) layer, while the second mirror layeris a p-type DBR layer; materials of the first mirror layer and thesecond mirror layer include AlGaAs with various Al mole percentages,wherein the oxide layer of the second mirror layer contains Al with arelative high mole percentage; the oxide layer at least extendshorizontally from an inner rim of the first isolation trench toward acenter of the mesa; the dielectric material is a polymer material withlow dielectric properties; and, the first contact layer and the secondcontact layer are both metal layers.
 8. The method of claim 6, whereinthe ion-implanted region is located in the second mirror layer, and theion-implanted region inside the mesa is located between the outputwindow and the first isolation trench by circling at least a portion ofa periphery of the output window.
 9. The method of claim 6, furtherincluding a step of forming a power output layer on the output window onthe top surface of the mesa.
 10. The method of claim 6, wherein a planeis formed at the bottom portion of the second isolation trench so as tohave the second contact layer to be in a horizon-extending state at thebottom portion of the second isolation trench.